The subject matter disclosed herein relates to steam turbines. More particularly, the subject matter relates to securing a closure bucket to a drum rotor in a steam turbine.
Steam turbine buckets, or blades, are often designed for installation on a turbine rotor wheel in a tangential direction. The buckets are typically attached to the turbine wheel using external circumferential dovetails, with a male dovetail on the wheel periphery and a complimentary female dovetail in the base or root of the bucket. In order to load these buckets onto the wheel, a notch which locally removes the male dovetail portions is cut on the periphery of the wheel, leaving a generally rectangular opening in the rotor wheel. Each bucket is then initially placed in the opening and then displaced tangentially onto and around the wheel. Once all the buckets have been loaded, a closure bucket (or “final bucket”) is placed in the opening, wherein grub screws are inserted through the rotor wheel to engage the closure bucket, thereby securing the closure bucket in the rotor wheel. The process of inserting grub screws and tapping threads to receive the screws is time consuming. In addition, the screws and threads are destroyed in situations where the closure bucket, or other buckets disposed on the rotor, need to be removed for maintenance. Thus, the grub screws can lead to challenging, costly, and time consuming assembly, repair, and reassembly of the rotor.